Apparatus for surveying boreholes



C. L. NORDEN APPARATUS FOR SURVEYING BOREHOLES Jan. 18, 1955 6 Sheets-Sheet l Filed Jan. 19. 1948 Heavy 5ml/ve Barre-RY Vma BY Lw ATTORNEY Barn-Rv l Jan. 18, 1955 c. L. NORDEN 2,699,611

APPARATUS FOR SURVEYING BOREHOLES Filed Jan. 19. 1948 6 Sheets-Sheet 2 INVENTOR ORNEY Jan. 18, 1955 c. L. NORDEN 2,699,611

APPARATUS FOR SURVEYING BoREHoLEs Filed Jan. 19, 1948 -46 Sheets-Sheet 5 FTEE llllllllllllllll IIIHIIIIHHI IN VEN TOR. Cfr/QL L. NQRDEN 54 HTT'ORNEY Jan. 18, 1955 c. L.. NORDEN APPARATUS FOR SURVEYING BoREHoLEs 6 Sheets-Sheet 4 Filed Jan. 19, 1948 308 INVENTOR. Cnam. L. NORDEN BVM A ATTORNEY Jan. 18, 1955 c. l.. NORDEN APPARATUS FOR suRvEYING BoREHoLEs 6 Sheets-Sheet 5 Filed Jan. 19, 1948 PLANE 0F HOP/ZON PL HNE OF HOD/ZON INVENTOR. Cam. L. /VOPDEN Jan. 18, 1955 c. L.. NORDEN 296991511 APPARATUS FOR sURvEYING BoREHoLEs Filed Jan. 19, 1948 lE5 Sheets-Sheet 6 PL HNE OF HOE/ZON PLQ/v5 NORM/7L To J 4X/S OF BO/QE HOLE INVENTOR.

CARL L. Ajo/QDE/v lfm L. SM

HTTO/VEY United States Patent O APPARATUS FOR SURVEYING BOREHOLES Carl L. Norden, New York, N. Y., assignor to The Norden Laboratories Corporation, White Plains, N. Y., a corporation o Connecticut Application January 19, 1943, Serial No. 2,975

9 Claims. (Cl. 33-205.5)

My invention relates to apparatus for surveying bore holes and more particularly to a device for measuring the inclination of bore holes from the vertical and the direction of the inclination in azimuth with reference to a selected direction. l

In the drilling of oil wells, the drill bit'must pass through many different geological strata having various physical characteristics. These differences frequently cause the bore hole to deviate from the vertical. In order to correct these deviations whipstocks are employed to bring the drill hole back to the desired direction.

Occasionally the geographical terrain is such that the location of the oil deposits is so positioned with respect to available drilling locations that it is desired to drill a hole having a determined azimuth and inclination from the drilling location in order to arrive at the desired oil bearing strata antecedently revealed by geological exploration.

The problem of surveying a bore hole in order to produce a record of deviations at various depths giving the direction of the inclination and its amount is exceedingly ditcult. This is especially true since modern practice involves the drilling of wells many thousands of feet in depth. Furthermore, lthe diameter of the hole is limited so that the surveying instrument must occupy a space of limited cross-sectional area.

The measuring of the amount of inclination presents no great problem and this can be done readily by means of levels and pendulums together with any appropriate means of making a record. The direction of inclination, however, has presented a problem which has not been satisfactorily solved. The use of magnetic compasses has been found to be unsatisfactory and unreliable due to errors introduced by magnetic disturbances which cannot be predicted and the magnitude and direction of which are usually unknown. Then, too, wells are frequently provided with casings which provide a complete magnetic shielding so that a magnetic compass is substantially useless.

Many attempts have been made to use gyroscopes to produce a reference direction from which deviations could be measured. Due to precession of gyroscopes caused by friction and the rotation of the earth on its axis the readings obtained have been unreliable since all of the gyroscopes known to the prior art will drift due to precession caused by friction and by the rotation of the earth.

One object of my invention is to provide an apparatus for surveying bore holes which eliminates the disadvantages of the prior art.

Another object of my invention is to provide an improved apparatus for surveying bore holes to determine the amount of inclination and its direction with reference to any predetermined reference direction.

Another object of my invention is to provide an apparatus for surveying bore holes in which a true reference direction is accurately and constantly maintained.

A further obiect of my invention is to provide an apparatus for surveying bore holes in which a record of the angle of inclination from the vertical and the direction oi inclination is made.

Other and further objects of my invention will appear from the following description:

in general my invention contemplates the provision of a casing having an outside diameter such that it may be readily lowered into a bore hole and ralsed therefrom.

lCC

The casing is fluid tight and of sufficient strength to withstand any pressures encountered within the bore hole. These pressures may be increased by the use of mud laden fluids such as are currently used in 'the drilling of deep wells.

The casing contains a camera unit of any appropriate design such as known to the art for taking photographs of a scale unit at periodic intervals. The scale unit may record the inclination, its direction, the time and the temperature. An azimuth scale is actuated by a gyroscope. The gyroscope is one in which the axis of spin is generally horizontal. Means are provided for maintaining the axis of spin in the predetermined plane. The predetermined plane may be the plane of the horizon, that is, a plane normal to true gravity or a plane normal to the axis of the bore hole at the position of the instrument. I accomplish this by introducing correctional precessions of the gyroscope by means of a servomotor and a switch. Error in azimuth introduced by the earths rotation on its axis is corrected by means of a precession weight adapted to produce a rate of precession in the proper direction as a function of its latitude of the place in which the surveying is being conducted.

Power to operate the gyroscope, the servomotor and the recording camera is provided from a battery contained within the unit. The use of a self-contained unit avoids many of the disadvantages of the prior art in which current leads from the surface have been attempted to be employed. It has been found that in such cases not only is the surveying costly and cumbersome7 but short circuits frequently occur due to the migration of fluids along the current-carrying conductors.

The accompanying drawings which form part of the instant specification and which are to be read in conjunction therewith and in which like reference numerals are used to indicate like parts in the various views:

Figure 1 is an elevation of a unit embodying my apparatus for surveying bore holes with a part broken away.

Figure 2 is a sectional view on a large scale with part of the casing removed, taken generally on the line 2-2 of Figure 1.

Figure 3 is a sectional view taken on the line 3-3 of Figure 2.

Figure 4 is an elevation taken on the line 4 4 of Figure 2 with the casing and housing removed.

Figure 5 is a fragmentary bottom plan view with parts in section taken along the line S-S of Figure 4.

Figure 6 is a sectional view on an enlarged scale taken on the line 6 6 of Figure 3.

Figure 7 is a sectional view on an enlarged scale taken on the line 7-7 of Figure 3.

Figure 8 is a fragmentary sectional view taken on the line 8-8 of Figure 6.

Figure 9 is a sectional Figure 3.

Figure 10 is a fragmentary sectional View drawn in an enlarged scale taken along the line 10-10 of Figure 2.

Figure 1l is a diagrammaticview showing the electrical circuits involved. Figure 12 is a diagrammatic view in perspective, showing the generation of corrections when the spin axis of the gyroscope is maintained in the plane of the horizon.

Figure 13 is a plan view of the diagrammatic view shown in Figure 12.

Figure 14 is a diagrammatic elevation showing the generation of corrections when the spin axis of the glyoscope is maintained normal to the axis of the bore Figure 15 is the Figure 14.

More particularly, referring now to the drawings, a casing 12 having an outside diameter such. that it may be lowered into the bore hole to be surveyed is provided with a removable bottom 14 which may be of any appropriate shape and a removable top 16. In a typical case, the casing 12 may have an outside diameter of 31/2 inches and be formed with a wall thickness of QG of an inch. An appropriate attachment by which the assembly is lowered, such as an eye 18, maybe secured to the casing top 16 by means of straps 20.

view taken on the line 9-9 of plan view of the diagram shown in The parts of my assembly are lodged in suitable housings which are assembled within the casing. The lowermost housing 22 is provided for the battery which may be of any appropriate design such as a plurality of dry cells or a storage battery to provide the desired voltage. The particular voltage is a matter of choice with the designer and I have found that E. M. F. of from 6 to 12 volts may be used. The gyroscope proper is lodged within housing 24 above which is a housing 26 for'the scale unit. The camera unit is situated within a housing 28. I provide separators 30 between adjacent housings within the casing. The assembly may be -made either from the top of the casing or from the bottom thereof or from both ends. Between housing 22 for the battery and housing 24 for the gyroscope unit, I provide a housing 32 containing a heavy spring for cushioning the assembly and absorbing shocks during handling and lowering.

Referring now to Figures 3 and 7, the gyroscope rotor 34 is designed to have the maximum moment of inertla for the space occupied. Accordingly, the rotor is made of very heavy metal such as tungsten which is pressed upon the steel disk 36. The disk 36 is secured to the gyroscope shaft 38 which carries an armature winding 40.

The shaft 38 is mounted in ball bearings 42 and 44 and is adapted to revolve at speeds between 12,500 and 15,000 revolutions per minute. The ball bearings are mounted in the gyroscope housing 46 which is in turn pivoted about ball bearings 48 and 50 carried by stub shafts 52 and 54. The stub shafts are aligned at right angles to the axis of the shaft 38 and are carried by the Cardan ring 56.

Current supply to the gyroscope motor winding 40 is by way of brushes 58 and 60 through commutator 62. A tubular member 64 is carried by the housing 46 and extends into the gyroscope rotor 34 as can readily be seen by reference to Figures 3 and 7. Pole pieces 66 and 68 are carried by the tubular member 64 and support eld windings 70 and 72.

The Cardan ring 56 is mounted for rotation about a normally vertical axis in upper ball bearing 74 and lower ball bearing 76 as can readily be seen by reference to Figures 2 and 3. For purposes of convenience the axis of shaft 38 around which the gyroscope rotor 34 revolves will be referred to as the spin axis. The axis through which stub shafts 52 and 54 pass, around which the gyroscope housing 46 pivots, will be referred to as the tilt axis. The vertical axis around which the Cardan ring 56 is pivoted will be referred to as the azimuth axis.

The lower Cardan bearing 76 is supported by the bottom member 78 of the housing 24. The member 78 is formed with a bracket 80 which carries a base plate 82, to which the housing 84 of a servomotor is secured. The motor shaft 86 of the servomotor is connected to the shaft 88 by means of a universal joint 90. The upper end of shaft 88 is formed with a flange 92 to which the Cardan ring 56 is attached in any suitable manner so that rotation of shaft 88 will rotate the Cardan in its bearings 74 and 76. It will be observed by reference to Figure 2 that shaft 88 is hollow. An insulating bushing 94 is carried by shaft 88 and supports a plurality of slip rings 96 through which electrical connection to the gyroscope motor is made. Carried by housing 32 and extending to the underside of member 78 of housing 24, I provide a cushioning spring 98 permitting relative motion between the upper assembly, comprising the rotor unit, the scale unit and the camera unit, and the battery unit against the, action of the spring in order to cushion the assembly from shocks which may be occasioned by the lowering of the assembly into a bore hole. The lower portion of servomotor housing 84 carries a guide member 100 extending through'a bracket 102. Downward movement of the upper sub-assembly compressing the spring 98 will permit the guide shaft 100 to pass through opening 104 in the housing 32 and opening 106 in the separator 30 covering the housing 22.

The upper portion of the Cardan ring 56 is secured to a tlange 108 similar to ange 92. The flange 108 is carried by a shaft 110 which rotates in the upper bearing 76. A disk 112 of light aluminum rests on a pin 115 carried by the upper end of shaft 110 and is clamped thereto by clamping nut 116. A cylindrical member 118 is carried by the disk 112 and is formed with an upper flange 120 which is calibrated in azimuth in any appropriate manner.

The Cardan ring 56 is formed with a boss 122, to which is secured by means of machine screws 124, a plate 126. A stub shaft 128 is carried by the Cardan 56, as can be seen by reference to Figures 2 and 5. A pendulum 130 is mounted for pivotal movement around bushing 132 carried by the stub shaft 128. The pendulum is provided with a hole 131 adapted to receive an immobilizing pin 135, as can readily be seen by reference to Figures 2 and 4. The end of the pin 135, in the interior of the hole 131, may be threaded. When the pin is in place, the pendulum is immobilized in a position to maintain the axis of the gyroscope at an angle to the axis of the instrument. The end of the stub shaft 128 carries a ball bearing 134 in which bearing and another ball bearing 136 carried by the plate 126, I pivot a short shaft 138. Secured to shaft 138 for rotation therewith, I provide a lever 140. A conducting arm 142 is secured to the lever 140 by means of screws 144 and is insulated therefrom by means of insulation 146. Carried by the pendulum and insulated therefrom by insulating member 148 are a pair of conducting segments 150 and 152. The end of conducting arm is normally adapted to rest upon the insulation 148 which separates the conducting segments and 152, as can be seen by reference to Figure 4.

If desired, the lever 140 may be made of insulating material. As can readily be seen by reference to Figures 4 and 7, an angle plate 15'4 is secured to the gyroscope housing 46 by means of a machine screw 156. A spring 158 is secured to the gyroscope housing 46 by means of a screw 160. A connecting rod 162 is fulcrumed around a pin 164 xed in plate 154 and maintained in connected position by the spring 158. A spring 166 is secured to the lever 140 by means of screw 168. The lower end of connecting rod 162 is fulcrumed around a pin 170 carried by the lever 140 and maintained in coupled position by the spring 166 as can readily be seen by reference to Figures 4 and 5. The distance between the axis of shaft 54 and the axis of pin 164 is exactly the same as the distance between the axis of bearing 136 and the axis of pin 170. The distance between the axis of shaft 54 and the axis of bearing 136 is exactly the same as the length of the connecting rod between the axis of pin 164 and the axis of pin 170. It will be seen that I have provided a parallel motion whereby the lever 140 will always be parallel to the spin axis of the gyroscope. Relative movement between the spin axis and gravity as represented by the pendulum will cause relative motion of contact arm 142 with respect to the conducting segments 150 and 152.

If desired, the pendulum 130 may have its upper part made. of insulating material and the weight obtained by securing a heavy member 131 to the upper portion of the pendulum by means of screws 133.

The upper portion of the scale housing 26 is closed by a member 172 formed with a central opening 174 in which is seated a heavy glass plate 176. The center of the glass plate 176 has a ground opening in which I seat a ball bearing 178. This bearing will cause a shadow cone. at the base of the scale compartment, and accordlngly I place all indicators, scales and the watch outs1de of the shadow cone. A shaft 180 carries a spherical bearing member 182 which rests upon the balls of the ball bearing 178. A shaft 184 is supported by the shaft by means of pins 186 or in any other suitable manner. A base 188 for supporting the scales and indicators is screwed to the lower end of shaft 184 by means of screw threads 190. As can readily be seen by reference to Figures 6 and 8, a bracket 192 is attached to the base by means of machine screws 194. Mounted upon the bracket 192, I provide a thermometer 194' which may be calibrated to temperatures as high as 300 F. The

- shaft 184 is formed with a bearing 196 in which is pivoted a shaft 198. Secured to shaft 198 for rotation therewith, I provide a pendulum 200 having a scale 202 which may be calibrated to show inclinations up to 40. A pointer 204 supported by the thermometer support 206 coacts with the pendulum scale 202 to enable the large inclinations to be read.

Likewise secured to the base 188 in any suitable manner is a bracket 207 in which is formed a raceway 208 which is provided with a lapped steel surface. Lodged within the raceway is a steel ball 210 which is dark blue for ease in reading. The ball which may be 3/32 of an inch or smaller is retained in the raceway by a retaining strip 212. Pins 214 and 216 prevent the ball from rolling out of the curved raceway. A ange 218 adjacent the ball is calibrated to inclinations up to A ball indicator is also mounted upon the base 188. As can be seen by reference to Figure 2, it comprises a ball support 220 formed with a spherical lapped steel surface upon which a small ball 222, G of an inch or smaller in diameter, is adapted to roll. The ball is retained by means of a curved glass cover 224. The glass cover is held in place by means of a casing 226. The ball support 220 is secured to the base 188 by means ofy a screw 228. The curvature of the ball support 220 is such that it is adapted to indicate inclinations up to the vicinity of 71/2". The glass cover is provided with a plurality of circular etched lines 230, each positioned to indicate 1 of inclination in any direction. Radial lines 232 are spaced apart.

In addition to the thermometer and the scales just described, I mount a watch 234 to the base 188 by means of holding clips 236 and 238. The holding clip 238 carries a pointer 240 adapted to cooperate with the azimuth scale 120 to indicate azimuth.

A U-shaped guide member 242 is secured to the underside of the base 188 by means of screws 244 and 246, as can readily be seen by reference to Figure 9. The guide 242 is disposed around the clamping nut 116 which holds the azimuth scale to the shaft 110. The clamping nut is formed with a cylindrical exterior surface. A roller 248 is mounted for rotation about a shaft 250 carried by the base 188. The roller 250 is adapted to contact the nut 116. The interior sides of the guide member 242 are likewise adapted to contact the cylindrical nut 116. When the instrument is vertical; that is, when the ball 222 is in the center of its saucer-like race 220, the pendulum 200 will indicate zero and the ball 210 is likewise in a position indicating zero. The assembly of scales suspended from the ball bearing 178 is such that the roller 248 and the interior sides of the guide member 242 just clear the lateral sides of the nut 116. The base 188 is formed with a thickened portion 252, giving offset weight to the base on a line drawn through the axis of the roller 248 and the axis of the cylindrical nut 116.

The arrangement just described provides a friction damping arrangement permitting the base and scale assembly to stabilize at the low gravity position without undue oscillation. The base and all clinometers are quite pendulous due to the suspension I employ. As the instrument is inclined, the weight 252 will cause the base to rotate to a position where the portion of the base to which weight 252 is secured is lowest. The greater the inclination, the greater will be the the guide plate 242 against the nut 116.

The scale unit cover member 172 supports bases 254 and 256 in which are positioned incandescent lamps 258 and 260 adapted to illuminate the face of the scale unit. Mounted above the scale unit within housing 28, I provide a camera unit 262, the lens of which 264 is shown. The camera unit may be of any appropriate design and is well known to the art. A moving picture camera, for example, adapted to be run by an electric motor may be employed. If the well is unusually long it is preferable to take exposures at greater intervals than those taken by a motion picture camera. This is a matter of choice with the user.

Referring now to Figures 2 and 7, I mount a pair of guide members 268 and 270 upon the gyroscope housing 46. Guide member 268 extends vertically of the gyroscope housing in a direction parallel to the azimuth axis, as can be seen by reference to Figure 2. Guide member 270 extends horizontally in a direction parallel to the spin axis of the gyroscope, as can be seen by reference to Figure 7. Mounted for rotation within suitable bearings in the guide member 268, I provide a screw 272. A weight 274 is internally threaded and screwed upon the screw 272. The external shape of the weight 274 is such that it engages a portion of the guide member and is prevented from relative rotation therewith. An adjusting head 276 is secured to the screw 272 so that upon rotation thereof the weight 274 will be caused to move upwardly or downwardly. By means of the weight 274, l am enabled to raise or lower the center of gravity of the gyroscope housing and assembly to a point where it will coincide with the horizontal plane passing through the tilt axis.

Mounted for rotation within the guide member 270, I provide a screw 278 upon which is threaded a weight friction damping of 28.0. The weight 28.0 is adapted to coact with a portion of the guide member 270 so that relative rotation between it and the guide member is prevented. The screw 278 carries a scale 282 calibrated as a function of the cosine of latitude. A slot 284 is formed in the screw so that it and the scale may be rotated to move the weight 280 away from or toward the housing of the gyroscope. The construction of this weight is such that it produces a moment about the tilt axis which is a function of the distance of the center of gravity of the weight from the tilt axis and of the magnitude of the weight. The torque produced by the weight acting through the length of the lever arm of its position from the tilt axis will cause the gyroscope to precess in azimuth and is adapted to introduce a correction for the rotation of the earth, as will be pointed out hereinafter more fully.

Electrical connections are made through the gyroscope housing in the manner shown in Figure l0. An insulating ferrule 286 is internally threaded and screwed in a threaded opening formed in the gyroscope housing 46. A conducting cup-shaped metallic member 288 is adapted to clamp a conductor 290 between it and an insulating disk 292 under the action of a screw 294 threadedly seated within the insulating ferrule 286. An appropriate connecting member 296 to which a conductor 298 is attached is clipped or otherwise secured to the lower end of the screw 294 within the gyroscope housing. This, for example, is the mode in which current is conducted to the field windings 70 and 72 of the gyroscope motor. The electrical circuits involved are shown diagrammatically in Figure l1. A battery 380 has one of its terminals grounded at 302. Its other terminal is connected to a conductor 304 through which all of the electrical connections are made. Conductor 306 connects conductor 304 and the conducting arm 142. Conducting segment 150 on the pendulum 1384 is connected by conductor 308 to the field winding 310, the other end of which is connected by conductor 312 to the brush 314 of the servomotor 84. The brush 316 of the servomotor is connected to ground 318. The conducting segment 152 on the pendulum 138 is connected by conductor 320 to the winding 322, the lower end of which is connected by conductor 324 to the brush 314. It will be observed that when contact arm 142 is connected to segment 150, current will iiow through the eld winding 310 and thence through the armature of the servomotor. When the contact arm 142 is connected to the segment 152 current will flow through the iield winding 322 in a direction opposite from that in which it flowed through field winding 310. Accordingly, since the direction of the polarity of the eld with respect to the direction of the armature current is reversed, the servomotor 84 will run in one direction when contact arm 142 is in contact with segment 150 and in the opposite direction when conducting arm 142 is in contact with segment 152. Conductor 326 is connected to the brush 58 of the gyroscope motor 4t). Brush 60 is connected to ground 328. Field windings 7l) and 72 are connected to conductor 326 in series, current flowing from conductor 326 to ground 330. Current for the camera motor flows from conductor 3M through conductor 332 and'thence through the armature winding of the camera motor 334 to ground 336 and through the field winding 338 to ground 340. The incandescent lamps 258 and 260 are connected across conductor 304 and ground 342.

In use, when it is desired to employ the mode of operation in which the spin axis of the gyroscope is maintained in the plane of the horizon, the pin is removed from the housing to free the pendulum 138. The scale 282 is set for the latitude of the geographical position of the bore hole. The watch is wound and synchronized with a watch at the surface. The camera is loaded with film and the switch to the current supply of the camera and incandescent lamps is closed. As soon as it is ascertained that the gyroscope is up to speed and the azimuth scale has been oriented to the desired direction, the units are assembled as shown in Figure 1 and a lowering cable is attached to the eye 18. The instrument is then lowered, its position in depth being ascertained by a suitably calibrated lowering reel or by appropriate markings on the lowering cable or both. The depth readings furthermore are correlated with time by the synchronized watch on the surface.

The gyroscope will tend to remain fixed in space.

Friction about the tilt axis which is minimized by the use of ball bearings will produce a slight tendency for the gyroscope to precess in azimuth. The directional effect of the gyroscope, however, is sufficiently great to minimize the small precessional force occasioned by slight friction about the tilt axis so that my gyroscope will indicate true direction for a long period of time, much longer than the time consumed by lowering the instrument into a bore hole and removing it therefrom.

The bore hole is generally vertical. Due to friction of the bearings, there will be a relative precessional motion between the true vertical direction and a line normal to the horizontal plane passing through the spin axis so that in a free gyroscope employing no correcting means, the angle between the spin axis and the vertical azimuth axis will gradually become smaller, depending on the friction. When this occurs, the directional efiect of the gyroscope in azimuth is reduced and when the spin axis coincides with the vertical azimuth axis will become zero. In order to maintain the spin axis normal to a line passing through the center of the earth, that is normal to true gravity, I provide the pendulum 130 with the contact segments 150 and 152 in my construction. As soon as the tilt axis of the gyroscope forms an angle greater or less than 90 with the direction of true gravity as determined by the pendulum, contact arm 142 will make contact with either segment 150 or 152. These segments, it will be remembered, are carried by the pendulum 130. If the deviation is such as to bring contact arm 142 into contact with segment 152, a circuit will be completed to the servomotor 84 which will apply a torque around the azimuth axis in a direction to precess the gyroscope about its tilt axis until the spin axis is again normal to true gravity. The direction of the torque is predetermined by the direction of the spin of the gyroscope and the direction of the deviation. Torque in the opposite direction is applied around the azimuth axis when contact arm 142 makes contact with segment 150. The pendulum accurately defines the direction of gravityand accordingly I am enabled to maintain the maximum directional effect of the gyroscope in azimuth.

It is to be remembered that the gyroscope will maintain a fixed position with respect to space. As the earth rotates, the spatial direction and the terrestrial direction in azimuth will have a relative movement which at the equator is at the rate of per hour. In other words, a point on the equator of the earth moves at the rate of 15 per hour so that the direction from the first point to the pole will make an angle of 15 with the direction to the pole occupied by that point one hour later. At points between the pole and the equator the rate of change of direction with respect to space varies as a function of the cosine of latitude.

In order to enable my gyroscope to indicate a true terrestrial direction, it is necessary to precess the gyroscope in azimuth in a direction to compensate for the rotation of the earth. The direction of precession will be from the elevated pole towards west since the earth rotates on its axis from west towards east. If, for example, the latitude of a place at which the bore hole to be surveyed is located were 4l-l0-0 north, the rate at which the gyroscope must be precessed in azimuth is l1-l7-24" per hour. Precession in azimuth is produced by torque applied around the tilt axis in a direction depending on the direction of spin. I accomplish this by means of the weight 280. The scale 282 is calibrated so that when it is set to the latitude of a place, the weight will occupy a position to cause a torque about the tilt axis to produce a precession about the azimuth axis in the correct direction at a rate which is represented by 15 cos. L per hour. Since my weight 280 is attached to the gyroscope housing on one side only, it will be necessary to change the direction of rotation of the gyroscope motor in south latitudes.

It will be seen that as the instrument is lowered into the bore hole, the Cardan 56 will remain in the alignment to which it was originally set. The azimuth scale 120 is carried by the Cardan so that it will remain in a fixed direction irrespective of any axial rotation of the instrument during lowering. As the instrument is inclined due to deviations from the vertical in the bore hole, the base 188 which carries the scales will rotate due to the weight 252. The weight 252 being offset fromV the axis of rotation of the base which is defined 8 by the line running through the axis of the upper beat*- ing 178 and the axis of the central nut 116, will cause the base to swing, the weight seeking the low side of the plane defined by the base. The roller 248 and the plate 242 will produce frictional damping tending quickly to stabilize the base in its low gravity position. The arrangement is such that the friction damping is proportionate to the angle of inclination since greater friction is produced by greater inclination when it is increasingly needed. The arrangement furthermore permits settling at low angles since the upper bearing friction is very small. The direction occupied by the weight will be indicated by the pointer 240 which cooperates with the azimuth scale 120. At small angles the true direction of the inclination may not be accurately indicated by the pointer 240. The position of the ball 222, however, will accurately indicate the true direction of the low point. The azimuth lines 232 on the level cooperating with the ball 222 will accurately show the correction to be applied to the reading given by the pointer 240. If the ball is in alignment with the azimuth mark aligned with the pointer 240 the correction is zero. If the ball is not in alignment with this azimuth mark, a

.correction must be made to the azimuth reading depending on amount and direction of the deviation in azimuth. The ball 222 indicates deviations in inclination up to 61/2. When the inclination is over 7 it must be read by the ball 210 cooperating with the scale 218. When the inclination is 20 it must be read by the pointer 204 cooperating with the scale 202. In most bore holes the inclinations will be less than 20 and for the greater part less than 7. It will be observed further that the ball 222 will indicate universal direction so that if the base is not aligned with true gravity, the inclination and the direction may be read. At all inclinations over 61/2" the directional effect of the weight 252 is sufficiently great so that both scales 202 and 218 will be aligned with true gravity. The clearance between the glass cover plate 224 upon which is etched the azimuth and inclination marks, is sufficiently close to the ball 222 so that substantially no parallax is introduced. A table of corrections for parallax may be provided. Parallax is occasioned by the fact that the lens 224 is slightly iffstt from the position of the casing 226 of the universal eve Referring now to Figures 12 and 13, it will be seen that the gyroscope remains oriented in a true direction from a predetermined reference direction which may be north if desired. If the bore hole forms an angle with the direction of true gravity, the plane of the azimuth scale will form a like angle with the plane of the horizon. Let this angle be It will be appreciated that I may represent the plane of the horizon and the azimuth plane as a pair of circular planes intersecting along a common line which is the axis ltlilt. Such a representation is shown in Figure 13 in w ic OA is a line lying along the line of intersection of the plane of the horizon and the plane of the azimuth scale, which line of intersection is the axis of tilt;

OB represents the true reference direction which is measured in the plane of the horizon;

OC, which represents the indicated reference direction in the plane of the azimuth scale, is a line from the center of the plane of the azimuth scale to a point C at which a line BC from point B perpendicularly intersects the plane of the azimuth scale;

OD represents the true direction of maximum tilt in the plane of the horizon;

p equals the angle between the axis of tilt and the true reference direction measured in the plane of the horizon;

' represents the angle between the tilt axis and the indicated referenc'e direction measured in the plane of the azirnnth scale;

is the angle of tilt which is measured around the tilt axis.

The angle between the reference direction OB, measured in the plane of the horizon, and the direction OD, measui'ed in the plane of the horizon, represents the angular direction of maximum tilt. It will be understood that the direction OD is always at right angles to the axis of tilt OA. Consequently, in the representation of Figure 13 the angle between the true reference direction OB and the true direction of maximum tilt OD is the complement of 19 the angle 11. If the angle qb can be determined,the true direction of maximum tilt may readily be obtained. It is to be understood that the angle qt in the plane of the horizon will always be greater than the angle ip in the azimuth plane. This is true no matter in what quadrant the reference direction lies and irrespective of the direction in which the azimuth plane is tilted with respect to the plane of the horizon. It will be remembered that the line BC in Figure 13 emanates from point B and is perpendicular to the azimuth plane at point C. If I pass a plane through line BC perpendicular to the axis of tilt OA at point A, the following relations appear from the figure:

AB 1 (5) eos I may therefore write:

tan (6) Tan (p CGS From the scale readings of the instrument, the angle q which is the angle between the axis of tilt and the reference direction measured in the plane of the azimuth, as well as the angle of tilt may readily be observed. By substituting the observed values in Formula 6 the angle qb, which is the angle between the axis of tilt and the true reference direction measured in the plane of the horizon, may be obtained. With this angle qb the true direction of maximum tilt may be obtained by determining the compiement of the angle g5.

If we place the pin 135 through the housing 24 with the end of the pin lodged in the hole 131 formed in the pendulum 130, we will lock the pendulum in a position parallel to the axis of the instrument. Any inclination of the instrument will cause the brush or the contact point carried by the arm 142 to make contact with either of segments 15) or 152, causing the servomotor 84 to apply a torque around the azimuth axis to precess the gyroscope about a tilt axis until the spin axis is normal to the axis of the instrument; that is, the axis of the bore hole. In most bore holes, the direction indicated by the azimuth scale will be the true direction and it will be unnecessary to apply the correction for angularity between the azimuth scale and the horizon which was described above.

Where, however, the bore hole is generally helical in shape, there will be a gyratory motion of the instrument around a vertical axis. Due to the fact that the Cardan is insensitive to rotation about any axis at right angles to the Cardan axis, an error will be introduced by the gyratory motion if the pendulum is locked to the gyroscope housing.

Referring now to Figures 14 and 15, the line A indicates the direction of true gravity. The line A' indicates the axis of a bore hole B. It will be remembered that the Cardan axis is locked to the gyroscope housing and, since the instrument must align itself with the bore hole, the Cardan axis will coincide with the axis A' of the bore hole. Let .w represent the angular velocity around the axis of true gravity A. At any given time t the angular velocity w results in an instantaneous angular displacement =.wt. Let represent the angle betwen the axis of the bore hole A and the direction of true gravity A. Let g5 represent the angle, measured in the plane of the horizon, between the tilt axis and the tine reference direction. Let fp' represent the angle, measured in the plane normal to the axis of the bore hole, between the tilt axis and the indicated reference direction. Since the difference between the true reference direction and the indicated reference direction is the result of the insensitivity of the Cardan to rotation about axes at right angles to the Cardan axis, the direction will be in error. Under the conditionwhere there is both a tilt and an angular velocity .w about the axis of true gravity, the indicated direction differs from the true direction. If the Cardan axis is aligned with the direction of true gravity so that the. degreveof tilt is zero, there will be no component of rotation about any axis at right angles with the Cardan axis. The error, therefore, will be zero. Similarly, if there is a tilt but it is constant so that there is no angular velocity w around the axis of true gravity, there can be no error introduced. An equation which satisfies the foregoing conditions and expresses the relation between the true reference direction measured in the plane of the horizon and the indicated reference direction measured in a plane normal to the axis of the bore hole is:

Collecting terms, substituting qb for wt and transposing, I may write:

The difference in direction Aga; that is, the error of the indicated direction from the true direction at any given point in the bore hole, may be represented by the following equation. i

where :p1 is the true direction at the point in the bore hole at which the measurment is started and qbz is the true direction at the point in the bore hole at which the measurement ends. It is readily apparent that since qb', which is the angle between the axis of tilt and the indicated reference direction measured in a plane normal to the axis of the bore hole, and the amount of tilt at any point in the bore hole, are known, the angle qb, which is the angle between the axis of tilt and the true reference direction measured in the plane of the horizon, may readilybe calculated from Equation 8. The direction of maximum' tilt is the complement of the angle qb.

Generally, it is simpler to use the tirst method; that is, the method employing the free pendulum where the bore hole is helical and there is to be gyratory motion of the instrument about a vertical axis. If the inclinations of the bore hole are in the same vertical plane, it is simpler to employ the second method in which the pendulum is locked to the gyroscope housing.

It will be seen that I have accomplished the objects of my invention. I have provided an improved apparatus for surveying bore holes in which the direction of inclination is indicated by reference to an azimuth scale oriented by a gyroscope, which gyroscope is corrected to precess in accordance with the component of the rotation of the earth on its axis depending upon the latitude of the place. I have provided means for maintaining the maximum directional effect of the gyroscope by precessing it about the tilt axis so that the spin axis will always lie in a plane normal to true gravity or in a plane normal to the axis of the bore hole being surveyed. I have provided means for aligning clinometers with true gravity where inclinations are in excess of about 5. I have provided additional means for accurately indicating inclination and direction where the inclinations are ,less than 5. A photographic record of the inclinations and directions of inclination may be made constantly or at predetermined intervals. My unit is a self-contained unit whereby the power to operate the component parts is housed within. the unit itself.

It will be understood that certain features and subcombinations are of utility and may be employed without reference to other features and sub-combinations. This is contemplated by and is within the scope of the claims. It is further obvious that various changes may be made in details within the scope of the claims without departing from the spirit of the invention. l t is, therefore, to be understood that this invention is not to be limited to the specific details shown and described.

Having thus described my invention, I claim:

1. An apparatus for surveying bore holes including in combination a gyroscope having a spin axis, a suspension for said gyroscope including a Cardan ring, means for maintaining the spin axis of said gyroscope in a predetermined plane, an azimuth scale carried by said Cardan ring, a pendulum having a base, a spherical bearing for rotatably suspending said pendulum, means adjacent the 11 base of said pendulum for limiting its swinging movement, a weight carried by said base eccentric to the axis of said pendulum, and an inclinometer carried by said pendulum.

2. An apparatus as in claim 1 in which said inclinometer comprises a second pendulum mounted for swinging movement about an axis extending at right angles to the axis of said rst pendulum and indicating means associated with said second pendulum carried by said base.

3. An apparatus as in claim 1 in which said inclinometer comprises a level carried by said base.

4. An apparatus as in claim 1 in which said inclinometer is mounted on said base.

V5. An apparatus as in claim 1 in which said means for limiting the swinging movement of said base comprises damping means for damping the rotation of said base.

6. In a device of the characterrvdescribed, deviation indicating means comprising a pendulum having a base, a spherical bearing for rotatably suspending said pendulum, a Weight carried by said base eccentric to the axis of said pendulum, means for limiting and damping the swinging movement of said base including a friction member carried by said base adapted to contact a stationary part, and means for positioning said friction member adjacent said stationary part, the construction being such that the greater the inclination, the greater will be the friction damping of the pendulum.

7. Apparatus for surveying bore holes comprising in combination a gyroscope, a Cardan ring providing a suspension for said gyroscope, a pendulum having a base, means for supporting said pendulum for pivotal and rotational movement and damping means mounted on the base of said pendulum, said damping means exerting a damping force which is directly proportional to the degree of inclination of said pendulum.

8. Apparatus for surveying bore holes comprising in combination an elongated casing, a gyroscope suspended within said casing, a Cardan ring providing a pivotal suspension for said gyroscope, a pair of rotatably mounted axial shafts for supporting said Cardan ring, a cylindrical axial scale fixedly mounted on kthe upper one of said 12 pair of axial shafts, spherical bearing means mounted centrally of said casing, a shaft suspended by one end from said bearing means, a pendulum mounted on the opopsite end of said suspended shaft, indicating means on said pendulum for indicating azimuth when the apparatus is in operation and frictional damping means mounted on said pendulum to damp the swing of said pendulum.

9. Apparatus for surveying bore holes according to claim 8 wherein a clamping nut is provided to retain -said azimuth scale on the upper one of said pair of axial shafts and said damping means includes a friction wheel mounted on said pendulum for cooperation with said clamping nut to damp the oscillations of said pendulum such that the damping force is directly proportional to the degree of tilt of the apparatus.

References Cited in the file of this patent UNITED STATES PATENTS 845,875 Lewis Mar. 5, 1907 1,124,068 Smitt Jan. 5, 1915 1,230,258 Wood June 19, 1917 1,553,990 Crisp Sept. 15, 1925 1,732,397 Braibant Oct. 22, 1929 1,812,994 Sperry July 7, 1931 1,837,479 Pew, Jr., et al. Dec. 22, 1931 1,912,768 Gilbert June 6, 1933 1,916,301 Cole July 4, 1933 1,924,816 Sperry, Jr. Aug. 29, 1933 1,947,562 Marmonier Feb. 20, 1934 1,959,141 Sperry, Jr. May 15, 1934 1,988,521 Sperry Jan. 22, 1935 2,190,790 Humphreys Feb. 20, 1940 2,220,055 Fischel Oct. 29, 1940 2,313,168 Opocensky Mar. 9, 1943 2,317,632 Miller Apr. 27, 1943 2,410,473 Weems Nov. 5, 1946 FOREIGN PATENTS 14,780 Great Britain of 1915 JAP... 

